Actuator for disk drive

ABSTRACT

An actuator for positioning a head with respect to a disk rotatably supported by a base plate in a disk drive assembly, including an actuator arm mounted on the base plate for supporting the head, and an electromagnetic assembly including the base plate for positioning the head with respect to the disk. The electromagnetic assembly includes a first magnet for providing a first magnetic field, the actuator arm includes a coil for passing an electric current in the magnetic field, and the base plate functions as a portion of a return for the magnetic field. A top plate mounted on the base plate supports a second magnet, which provides a second magnetic field, and the coil has portions in the first and second magnetic fields. A center pole extending through the coil, supports for holding the center pole between the top and base plates, and the top and base plates function as returns for the first and second magnetic fields.

This application is a continuation of Ser. No. 07/342,716 filed April24, 1989, which is a continuation of Ser. No. 056,602, filed May 29,1987, now abandoned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is related to the following Applications, all assignedto the Assignee of the subject Application:

1) ACTUATOR FOR DISK DRIVE, inventor Frederick Mark Stefansky;

2) LATCH MECHANISM FOR DISK DRIVES, inventors Frederick Mark Stefanskyand Glade N. Bagnell;

3) DISK DRIVE SYSTEM CONTROLLER ARCHITECTURE, inventors John P. Squires,Tom A. Fiers, and Louis J. Shrinkle;

4) DISK DRIVE SOFTWARE SYSTEM ARCHITECTURE, inventors John P. Squires,Tom A. Fiers, and Louis J. Shrinkle; and

5) DISK DRIVE SOFTWARE SYSTEM ARCHITECTURE UTILIZING IMBEDDED REAL TIMEDIAGNOSTIC MONITOR, inventor John P. Squires.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an actuator for a disk drive.

2. Description of the Related Art

Developments in personal computers, portable computers and lap topcomputers have prompted reductions in the size and increases in memorycapacity of disk drives. Existing disk drives, however, suffer fromseveral disadvantages, and attempts to provide further reductions insize, and weight and increases in durability and memory capacity havebeen hampered by these disadvantages.

Existing disk drives require a large number of mechanical parts. Eachadditional part in a disk drive represents an increase in thepossibility and probability of the mechanical failure of the driveFurthermore, each part in a disk drive represents an increase in theweight of the drive and the space occupied by the drive, and thedecrease in the ability of the drive to survive physical shocks andvibrations.

Resistance to physical shocks and vibrations is critical to protectingthe disk or disks, the head or heads, and the various bearings in a diskdrive from damage; in particular, damage to the disks which can cause aloss of data, and damage to the heads or the bearings which can end thelife of a drive, resulting in a total loss of data. Prior disk drives,however, have limited resistance to physical shocks.

Another problem with prior disk drives is the difficulty in sealing thedrive to protect the disks from contaminants. This difficulty arisesfrom the large area which must be sealed to protect the environmentwhere the disk resides and from the large number of points at whichaccess is provided to the environment in which the disk resides. Theseaccess points are utilized to bring to the interior of the disk driveelectrical circuits which provide current to the motor which rotates thedisk, transmit data signals to and from heads which read and recordinformation on the disks, and in some instances, provide current to avoice coil for positioning the head (or heads) with respect to the diskor disks.

Many of these disadvantages of prior disk drives are attributable to thecasing--a three-dimensional casting or so-called "toilet bowl"--in whichthe disks reside. Such a casing is a large, three dimensional piece ofcast metal, usually aluminum, having a round portion where the disksreside--hence the name "toilet bowl." A top plate covers the entire opentop of the casing, forming a seal therewith. The seal between the casingand the cover has a large area due to the large opening at the top ofthe casing. Furthermore, the spindle on which the disks rotate extendsthrough both the casing and the cover.

Both the seal and the protrusion of the spindle through the casing andthe cover provide possible points of entry for contaminants. Further, indisk drives using stepper motors to position the heads with respect tothe disk, the stepper motor is located outside of the casing, requiringanother seal between the stepper motor and the casing. Acknowledging theexistence of points where contaminants can enter the disk drive,manufacturers of conventional disk drives provide a breather filter anddesign the disk drives so that the rotation of the disks causes the diskdrives to exhaust air through leaks in the seals and to intake air onlythrough the filter provided in the breather filter. However, a fairlycourse filter must be provided in the breather filter for a flow of airto exist, and thus contaminants can enter the disk drive through thefilter paper.

A cast casing is difficult to manufacture with precision, particularlythe location of mounting points for elements of the drive supported bythe casing. Mounting holes must be drilled after the casing is cast, andthe mounting holes must be aligned with the casing and with each other.More importantly, however, a three-dimensional, cast casing flexes dueto thermal stresses. Flexing of the casing causes tracking problems bymoving the heads, which are mounted at one point on the casing, relativeto the disk, which is mounted at another point on the casing. Inmulti-disk disk drives the heads associated with different disks canmove relative to the disks to the point where different heads are indifferent cylinders--a cylinder being defined as a vertical segmentrepresenting the same track on the respective disks. This problem iscompounded by increased track densities.

An additional problem associated with known disk drives is theirsusceptibility to damage caused by physical shocks. This susceptibilityto damage is attributable, at least in part, to the fact that thespindle on which the disks rotate is mounted directly to the castcasing.

In conventional disk drives having a cast casing and utilizing a voicecoil to position the head with respect to the disk, the voice coil is aunit with a large number of elements including a permanent magnet toprovide a magnetic field, separate pieces of magnetically permeablematerial which provide a return for the magnetic field, and a coil forcarrying an electric current; the aluminum casing is not magneticallypermeable and cannot be utilized as a return for the magnetic field. Theseparate pieces of magnetically permeable material add weight andcomplexity to the disk drive and require additional space. Further, thepermanent magnet is mounted vertically, i.e., in a plane perpendicularto the plane of the disks, and to maintain a constant spacing betweenthe magnet and the coil, which is mounted on a pivoting arm, the magnetmust be curved, increasing manufacturing cost and difficulty.

Various types of locking (or latch) devices have been used to lock thearm of a voice coil in a particular position when the disk drive is notoperating. The trend in latch devices is to utilize a high power unitwhich is separately assembled to provide reliability. However, highpower latch devices generate a large amount of heat which is notdesirable in a disk drive or any other area in a computer. Further, theoperation of conventional latch devices can be position dependent. Thus,the orientation of the disk drive could effect the reliability of thelatch device.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anactuator for a disk drive assembly which does not require extra elementsto provide magnetic returns and which creates the largest possible forcefor accelerating an actuator arm.

A further object of the present invention is to provide an actuatorutilizing a base plate, which supports the disk and the actuator, as amagnetic return.

Another object of the present invention is to provide an actuator whichutilizes flat magnets.

Another object of the present invention is to provide an actuator whichachieves short seek times.

Another object of the present invention is to provide an actuator whichallows a head to access a large number of tracks per inch.

The present invention is directed to an actuator for positioning asensor with respect to a disk supported by a base plate in a disk driveassembly, comprising an actuator arm mounted on the base plate forsupporting the sensor, and electromagnetic means including the baseplate for positioning the sensor with respect to the disk. A top platemay be mounted on the base plate and the actuator arm supported betweenthe top and base plates, in which case the electromagnetic means alsoincludes the top plate.

The electromagnetic means includes a magnet on the base plate forproviding a first magnetic field, a coil attached to the actuator armfor passing an electric current in the magnetic field, a center poleextending through the coil, and support posts supporting the center poleon the base plate. The plate may be mounted on the base plate and theactuator arm pivotably mounted between the top and base plates, in whichcase the electromagnetic means also includes a magnet on the top platefor providing a second magnetic field and support posts for supportingthe center pole form the top plate. The top plate, the center pole, andthe support posts between the center pole and the top plate function asa return for the second magnetic field.

A specific advantage of the present invention is that the top and baseplates function as magnetic returns, and consequently separate pieces ofmagnetically permeable material are not required to provide magneticreturns.

Another advantage of the present invention is that the magnets can beflat rather than curved, and that the magnets can be mounted directly onthe top and base plates rather than on a support holding the magnetperpendicular to the casing of the disk drive.

Another advantage of the present invention is that the overall size,particularly the thickness, of the disk assembly can be reduced due tothe use of the top and base plates as elements in the actuator.

Another advantage of the present invention is that two portions of thecoil pass electric currents in two magnetic fields, creating largeforces on the actuator arm, and therefore reducing seek times.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-10 illustrate a first embodiment of the disk drive of thepresent invention. In particular:

FIG. 1 is an isometric view of a disk drive according to the firstembodiment of the present invention;

FIG. 2 is an exploded view showing the hard disk assembly, the shockframe, and the circuit board comprising the disk drive of the presentinvention;

FIG. 3A is a partial sectional view showing the mounting of the harddisk assembly to the shock frame and showing the mounting of the baseplate on the end plate;

FIG. 3B is a sectional view of the interface of the end plate and thecasing of the hard disk assembly;

FIG. 4 is partial cutaway view of the casing;

FIG. A is an isometric view of the end plate and the base plate;

FIG. 5B is a sectional view along line 5B--5B in FIG. 5A;

FIGS. 6A and 6B are plan views of the actuator assembly;

FIG. 7 cross sectional view for explaining the magnet fields in theelectromagnetic means of the voice coil assembly;

FIGS. 8A and B are top views of the actuator arm assembly, wherein FIG.8B is an exploded view of a portion thereof along line 8B in FIG. 8A;

FIG. 9A is a side view of the actuator arm assembly and a portion of theflexible circuit assembly;

FIG. 9B is a side, partial sectional view of the actuator arm assembly;and

FIG. 10 is an exploded view of the actuator assembly.

FIGS. 11-19 illustrate a second embodiment of the disk drive of thepresent invention. In particular:

FIG. 11 is an exploded, isometric view of a disk drive according to thesecond embodiment of the present invention;

FIG. 12 is a sectional view of the casing for the disk drive;

FIGS. 13A and B are sectional views showing the seal between the casingand the end plate;

FIGS. 14 and 15 are plan views of a portion of the hard disk assembly;

FIG. 16 is an exploded view of the actuator assembly;

FIG. 17 is a side, sectional view of the actuator arm;

FIG. 18 is a top, partial sectional view of the latch mechanism; and

FIG. 19 a side view of the latch mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Two embodiments of a disk drive according to the present invention willbe described with reference to FIGS. 1-19. The disk drive describedherein includes a hard disk assembly incorporating various numbers ofhard disks and utilizing Winchester technology; however, the disk driveof the present invention may utilize other types of disks, for example,optical disks, and other read/write technologies, for example, lasers.The diameter of the disks utilized in the disk drive of the presentinvention have a diameter on the order of 3.75 inches, or so-called "3.5inch" disks; however, the disk drive of the present invention can beused with any diameter disk whether larger or smaller than 3.75 inches.

A disk drive according to a first embodiment of the present inventionwill be described with reference to FIGS. 1-10.

As shown in FIGS. 1 and 2, a disk drive according to the presentinvention includes a disk assembly 26, a shock frame 27 on which thedisk assembly 26 is mounted, and a printed circuit assembly 28 mountedon the shock frame 27. Briefly, the disk assembly 26 includes an endplate 30, a base plate 32 mounted to the end plate 30, and a casing 34mounted to and forming a seal with the end plate 30 to provide acontrolled environment within the casing 34. Hard disks 36, two disks inthe first embodiment, are rotatably mounted to the base plate 32 via amotor 37 (FIG. 5A). An actuator assembly 38 includes arm assembly 40pivotably mounted between the base plate 32 and a top plate 42, the topplate 42 itself being mounted to the base plate 32. Outside diametercrash stop 44 and filter assembly 45 are mounted on the base plate 32,and latch 46 is pivotably mounted between the top and base plates 42,32.

The disk assembly 26 is mounted to the shock frame 27 via attachmentpoints 47a-b in the end plate and two posts 48a-b on the casing 34. Endplate attachment points 47a-b are attached to the frame 27 at mountingpoints 50a-b, respectively, and mounting tabs 48a-b are connected to theshock frame 27 at mounting points 50c-d. Each mounting point 50a-d onshock frame 27 has an aperture into which grommets 58 are inserted.Posts 48a-b on casing 34 are inserted directly into the grommets 58 inmounting points 50c-d, respectively, whereas shock spools 60 areinserted in the grommets 58 in mounting points 50a-b and mounting screws62 are inserted through the shock spools 60 and threaded into attachmentholes 47a-b of end plate 30.

The printed circuit assembly 29 (shown in an inverted position in FIG.2) is also attached to the shock frame 27. A single bus 52 carries allof the electrical signals from the printed circuit assembly 28 to thedisk assembly 26 via a connector 54 and header 56 in the end plate 30.Further, bus 52 has only twenty (20) pins due to the fact that a DCmotor requiring only three (3) leads is utilized. Such a motor isdescribed in U.S. patent application Ser. No. 880,754, entitled METHODAND APPARATUS FOR BRUSHLESS DC MOTOR SPEED CONTROL, filed July 1, 1986,inventors John P. Squires and Louis J. Shrinkle, assigned to theAssignee of the subject application.

The disk drive of the first embodiment of the present invention has thefollowing outline dimensions: Height 1.5" (3.81 cm); Length 5.75" (14.61cm); and Width 4.0" (10.61 cm), and a total weight of 1.2 pounds. Thus,the disk drive of the present invention is one-half (1/2) of the size ofa one-half (1/2) height 51/4 inch disk drive.

The interrelationship of the end plate 30, the base plate 32, and thecover 34, as explained below with reference to FIGS. 3-5, provides adisk assembly 26 with a resistance to distortion caused by physical andthermal stresses and provides a controlled environment within thecasing.

A seal is formed between the end plate 30 and casing 34 by a gasket 64.The partial, cross-sectional view of FIG. 3B shows the end plate 30, thecasing 34, and the gasket 64 when the seal is formed. Gasket 64 has asloped portion 64a which facilitates the assembly of end plate 30 andcasing 34. Specifically, the opening of casing 34 is designed to expandslightly as the edge of the casing 34 slides up the sloped portion 64aof the gasket 64. Screws 66 hold the casing 34 to the end plate 30, ando-rings 68 provide a seal around mounting screws 66 Gasket retainers 70(FIG. 5A) are provided at the top and bottom of end plate 30 to maintainthe proper positioning of gasket 64. It has been found that the gasketretainers 70 are necessary when the disk assembly 26 is placed in anenvironment where the pressure outside of the casing 34 is lower thanthe pressure inside casing 34, for example, at high altitudes. In suchsituations the pressure differential between the environments inside andoutside the casing 34 forces the gasket 64 to work its way out frombetween end plate 30 and casing 34.

The ability to seal the environment within the casing alleviates theneed for a breather filter and allows the disk drive of the presentinvention to use an internal air filtration system. The seal provided bygasket 64 is stable at pressures experienced at altitudes from 200 feetbelow sea level to 10,000 feet above sea level during operation of thedisk drive. The internal air filter 45 has an 0.3 micron filter toprovide a clean environment for the heads and disks.

As shown in FIGS. 3A and 5A-B, the base plate 32 is attached to the endplate 30 by mounting screws 72 which extend through mounting brackets74a-b of end plate 30. Each mounting bracket 74a-b includes a boss 76a-bhaving an axis parallel to the plane of the end plate. The base plate 32rests against bosses 76a-b and mounting screws 72 extend throughmounting brackets 74a-b and thread into plastic nuts 78. The plasticnuts 78 are formed of a semi-rigid material, for example, Delran 500,and have a sleeve 78'0 which extends through the base plate 32 andcontacts the bottom of the mounting brackets 74. The length of thesleeves 78' is greater than the thickness of the base plate 32 plus thedepth of the boss 76. This mounting system allows the base plate topivot with respect to the end plate about a line defined by the contactpoints of the bosses 76a-b and the base plate 32. The pivoting of thebase plate 32 with respect to the end plate 30 prevents the base plate32 from being twisted, flexed, or otherwise distorted when the baseplate 32 and end plate 30, as a unit, are attached to casing 34, therebyengaging notch 80 in base plate 32 with attachment point 82 (FIG. 4) ofcasing 34. Further, the base plate 32 may be manufactured by stamping, aprocess which enables the base plate and all of the mounting holestherein to be manufactured in a single step. Therefore, separate stepsotherwise necessary to align the mounting holes are avoided.

The structure and operation of actuator assembly 38 will be explainedwith reference to FIGS. 6-10. The purpose of the actuator assembly 38 isto position heads 84 with respect to the surfaces of the disks 36 bypivoting arm assembly 40. Specifically, its purpose is to position theheads 84 over individual tracks on disks 36. Arm assembly 40 includesflexures 86 for supporting heads 84, the flexures in turn beingsupported by actuator arm 88. Arm assembly 40 pivots on actuator post90, including a sleeve bearing, which is fixed to the base plate 32. Acoil 92 is provided on actuator arm 88 on the opposite side of actuatorpost 90 from heads 84. Arm assembly 40 is precisely balanced, i.e.,equal amounts of weight are provided on either side of actuator post 90,so that the positioning of heads 84 is less susceptible to linear shockand vibration.

The force utilized to pivot arm assembly 40 is provided by a voice coilassembly. The voice coil assembly includes coil 92, center pole 94 whichextends through coil 92, support posts 96a-b (each including lower andupper portions 96a₁, 96b₁, and 96a₂, 96b₂, respectively) for supportingcenter pole 94 between base plate 32 and top plate 42, first and secondpermanent magnets 98a-b respectively attached to the base plate 32 andthe top plate 42 below and above coil 92, and top and bottom plates 32,42. Top and base plates 42, 32 in conjunction with support posts 96a-band center pole 94 functions as returns for the magnetic fields providedby first and second permanent magnets 98a-b. In these returns for themagnetic fields it is important that there are no air gaps betweensupport posts 96a-b and either the base plate 32, the center pole 94, orthe top plate 42; any air gap would create a discontinuity in thereturn, greatly reducing the strength of the magnetic field in theportion of the return isolated from the magnet by the air gap.

The first and second magnetic fields B₁ (shown by the solid arrows) andB (shown by the dashed arrows) as contained by the returns areillustrated in FIG. 7. By providing returns for the first and secondmagnetic fields B₁, B₂, thereby containing the magnetic fields B₁ and B₂in the returns, the magnetic field intensity is increased in the regionbetween the center pole 94 and each of the magnets 98a-b, where thecurrent carrying coil 92 is positioned. The force on a current carryingwire in a magnetic field is proportional to the magnetic fieldintensity, and is expressed by the equation dF=idl×B, where F is theforce, i is the current, l is the length of the wire, and B is themagnetic field. Passing a current in opposite directions in coil 92provides respective forces F₁ and F₂ (FIG. 6A) normal to the plane ofthe windings of the coil and in opposite directions; these forces F₁ andF₂ pivot arm assembly 40 in opposite directions.

Crash stops are provided to limit the pivoting movement of arm assembly40 so that heads 84 travel between selected inside and outside diametersof disks 36. An inside diameter crash stop comprises an o-ring 100 (FIG.6A) fitted on support post 96a₁. When the pivoting motion of armassembly 40 places heads 84 at the inside diameter of the disks 36 aportion of the actuator arm 88 contacts inside diameter crash stop 100,thereby preventing further movement of the heads 84. FIG. 6A illustratesthe arm assembly 40 in a position near the inside diameter crash stop100. FIG. 6B illustrates the arm assembly 40 when a portion of actuatorarm 88 is in contact with u-shaped spring 102 of outside diameter crashstop 44. The u-shaped spring 102 (FIG. 2) is preloaded by bending thespring around three metal dowels 104a-c. Preloading spring 102 limitsthe deflection of the heads to approximately 40 thousandths of an inchbetween the first contact between actuator arm 88 and spring 102 and theposition at which motion of the arm assembly 40 is stopped.

The above-described structure of the disk drive of the present inventionprovides excellent protection from shock and vibration. In particular,the disk drive will withstand nonoperating shocks of 75g's and operatingshocks, without nonrecoverable errors, of 5g's. Nonoperating vibrationof 2g's in the range of 5-500 Hz is the specified tolerable limit.Operating vibration, without nonrecoverable data, is specified at 0.15g's for the range of 5-500 Hz.

Each of the two disks 36 has 752 tracks per surface due to the abilityof the actuator assembly 38 to operate with a track density of 1000tracks per inch. Thus, utilizing 26 blocks per track and 512 bytes perblock, the disk drive of the first embodiment has an unformattedcapacity of 50.1 MBytes and a formatted capacity of 40 MBytes. Theactuator assembly 38 provides an average seek time of 29 ms and atrack-to-track seek time of 10 ms. The average seek time is determinedby dividing the total time required to seek between all possible orderedpairs of track addresses by the total number of ordered pairs addressed.

Latch mechanism 46, which locks the actuator arm in an orientation wherethe heads 84 are positioned at the inside diameter of the disks 36, willbe described with reference to FIGS. 6, 7, and 10. The latch mechanism46 is balanced to pivot on metal dowel 106 which is affixed to the baseplate 32. When the air flow generated by the rotation of the disks 36 isnot great enough to overcome the biasing force of spring 110, which actsagainst spring post 112, the latch mechanism in 46 is held in the lockedposition by spring 110, as shown in FIG. 6A. When latch 46 is in thelocked position, latch tab 114 of the latch 46 contacts latch surface108 of actuator arm 88, thereby pinning the arm assembly 40 between thelatch tab 114 and the inside diameter crash stop 100. Accordingly, thearm assembly 40 is locked in an attitude where heads 84 are over nondataareas at the inside diameter of disks 36. The voice coil assembly pivotsthe arm assembly 40 to the position where the heads 84 are at the insidediameter of the disk before the rotational speed of the disks 36 isdecreased to the point where the heads 84 land on the disks 36. Thus,the heads 84 land only on the nondata area at the inside diameter of thedisks 36.

When the air flow generated by the rotation of the disks 36 is largeenough to pivot the latch mechanism 46 to the position shown in FIG. 6B,the arm assembly 40 is unlocked and able to pivot. To provide an airflow large enough to pivot latch mechanism 46, outside diameter crashstop 44 and filter assembly 45 are shaped to maintain a circular airflow inside the casing when the disks 36 are rotating, by preventing theair flow from escaping from the region over the disks 36. In addition,filter assembly 45 has an air intake (not shown) to pass the air througha filter medium (not shown), and the air exiting the filter assembly 45passes through a venturi, giving the exiting air a large velocity anddirecting the existing air flow directly at the latch mechanism 46. Thehysteresis of the spring force provided by spring 110 is carefullyselected so that the airflow generated by the rotation of disks 36overcomes the biasing force of spring 110 and pivots latch 46 to theunlocked position when the disks are rotating well below the fullrotational speed of, for example, 3600 RPMs, and so that spring 110biases the latch 46 to the locked position when the rotational speed ofdisks 36 slows just below full rotational speed; this relationshipassures that the latch mechanism 46 will always be unlocked due to theexcess airflow available for unlocking the latch mechanism 46, and thatthe arm assembly 40 will be locked at the inside diameter of the disks36 when the heads 84 land on the disks 36.

A flexible circuit assembly 116 for carrying electrical signals fromheader 56 to heads 84 and actuator assembly 38 will be described withreference to FIGS. 6A, 8A-B and 9A. The flexible circuit assembly isseparated into three portions A first portion 118 carries current tocoil 92 of actuator assembly 38. A second portion 120 is a ground planewhich separates the current carrying portion 118 from a third datacarrying portion 122. The data carrying portion 122 provides signals toheads 84 for recording information on disks 36 and carries signals fromthe heads to the printed circuit assembly 28, via header 56 and bus 52,when reading data from disks 36. Interference with the relatively weakdata signals which would otherwise be caused by the larger currentsnecessary to operate the actuator assembly 38 passing through the firstportion 118 of the flexible circuit assembly 116 is prevented by theprovision of ground plane 120.

The flexible circuit assembly 116 is parallel to the base plate at thepoint where it is connected to header 56; however, the flexible circuitassembly 116 passes through a 90 degree bend so that it is separatedinto segment 116a which is parallel to the base plate and segment 116bwhich is perpendicular to the base plate. Segment 116b of the flexiblecircuit assembly 116 is shown from the top in FIGS. 6A and 8A and fromthe side in FIG. 9A.

Any force exerted on arm assembly 40 by flexible circuit assembly 116affects the function of actuator assembly 38 in positioning heads 84with respect to disk 36, particularly the track following and seekfunctions described in the above-referenced applications entitled DISKDRIVE SOFTWARE SYSTEM ARCHITECTURE and DISK DRIVE SOFTWARE SYSTEMARCHITECTURE UTILIZING IMBEDDED REAL TIME DIAGNOSTIC MONITOR. The forceprovided by the voice coil assembly is corrected to compensate for theforce exerted by flexible circuit assembly 116. As the force exerted byflexible circuit assembly 116 increases, the variation of the force overthe range of motion of arm assembly 40 will have a greater variance, andtherefore accurate track following and seeking become more difficult.Accordingly, the radius R of the curve in section 116b of the flexiblecircuit assembly 116 (FIG. 6A) must be large enough so that the flexiblecircuit assembly 116 does not exert a large force against arm assembly40 to which it is attached.

In order to protect the disks 36--particularly the magnetic recordingmedium on the disks--from any magnetic fields which might be created bycurrents passing through leads 124, which carry signals from theflexible circuit assembly to the heads 84, leads 124 run on oppositesides of flexures 86 from the disk. In addition, at the point where theflexures are attached to the actuator arm 88 the leads 124 arepositioned in an indentation or groove provided in the edge of theactuator arm 88. A groove in the actuator arm is shown in the partialcutaway view of FIG. 8B. Thus, the disks 36 are always protected fromthe leads 124 by flexures 86 or by actuator arm 88.

A disk drive according to a second embodiment of the present inventionwill be described with reference to FIGS. 11-19. FIG. 11 shows the diskassembly 126 which is mounted on a shock frame (not shown) similar toshock frame 27 of the first embodiment. A printed circuit assembly (notshown) similar to printed circuit assembly 28 is also mounted on theshock frame. The mounting of hard disk assembly 126 on a shock frame andthe electrical connections between the hard disk assembly 126 and aprinted circuit assembly (not shown) are provided in a similar manner tothose described with respect to the first embodiment of the presentinvention. Therefore, these aspects of the second embodiment of thepresent invention will not be described in detail.

The disk drive of the second embodiment, having four (4) disks, isslightly taller (1.625"; 4.13 cm) than the disk drive of the firstembodiment; however, the length and width remain the same. The weight is2.0 pounds. The specified limits of shock and vibration for the diskdrive of the second embodiment are the same as that of the disk drive ofthe first embodiment.

Disk assembly 126 of the second embodiment includes an end plate 130, abase plate 132 mounted to the end plate 130, and a casing 134 mounted toand forming a seal with the end plate 130 to provide a controlledenvironment within the casing 134. In the second embodiment, four harddisks 136 are rotatably mounted on the base plate via a motor 137 (FIG.16) and actuator assembly 138 including arm assembly 140 is mountedbetween the base plate 132 and a top plate 142 which is mounted to thebase plate 132. In the second embodiment, top plate 142 and the baseplate 132 serve to rotatably support the disks 136.

The interrelation of the end plate 130, the base plate 132, and thecasing 134 will be described with respect to FIGS. 11-14. End plate 130is fastened to the casing 134 by four screws 150 which pull the casing134 towards the end plate 130. As the casing 134 is pulled toward theend plate 130, a gasket 152 (FIGS. 13A-B), positioned between the endplate 130 and the casing 134, is compressed and is squeezed into grove153 in end plate 130. Squeezing gasket 152 into groove 153 holds thegasket in place and eliminates the need for the gasket retainers 70utilized in the first embodiment. Pulling the cover 134 toward the endplate 130 also engages extension 154 of the base plate 132 with mountingpoint 156 in casing 134 (FIGS. 11-12), particularly with a plasticinsert 157 provided in mounting point 156.

To ensure that an even amount of pressure is applied at all points alongcircumference of gasket 152, the base plate 132 pivots with respect tothe end plate 130 in the plane of the base plate. The pivoting of thebase plate 132 is achieved by mounting the base plate 132 to the endplate 130 with a single mounting screw 158 (FIG. 14). The seal providedby gasket 154 is stable at pressures experienced at altitudes from 200feet below sea level to 10,000 feet above sea level.

The actuator assembly 138 of the second embodiment of the presentinvention, which is similar in structure and function to the actuatorassembly 38 of the first embodiment of the present invention, will bediscussed with reference to FIGS. 14-16. Again, the purpose of actuatorassembly 138 is to position heads 84 over individual tracks on the disks136; eight heads 84, one for each side of the four disks 136, are usedin the second embodiment. Arm assembly 140 includes heads 84, flexures86 for supporting the heads 84, and an actuator arm 160 for supportingthe flexures 86. The arm assembly 140 pivots on a bearing 162 which issupported between the base plate 132 and the top plate 142. A coil 164(shown in cross section in FIG. 18) is provided by actuator arm 160 onthe opposite side of bearing 162 from heads 84. As in the firstembodiment, the arm assembly 140 is precisely balanced so that it pivotseasily on bearing 162.

A voice coil assembly for pivoting arm assembly 140 includes coil 164,center pole 166 which extends through coil 164, center pole supports168a₁₋₂ -b₁₋₂, first and second permanent magnets 170a-b, and the topand base plates 142, 132. Returns for the magnetic fields of first andsecond permanent magnets 170a-b are provided by the center pole supports168, top and base plates 142, 132, and center pole 166. Passing acurrent in opposite directions in coil 164 provides forces F₁ and F₂(FIG. 14) which pivot arm assembly 140 in opposite directions. The pathsof the magnetic fields are similar to the magnetic field paths shown inFIG. 7 with respect to the first embodiment.

A flexible circuit assembly (not shown), similar to flexible circuitassembly 116 of the first embodiment, carries electrical signals fromheader 56 (FIG. 11) to coil 164 and heads 84.

The pivoting motion of arm assembly 140 is limited by dowel 178 whichfunctions as an outside diameter crash stop, and by an o-ring 180 fittedaround center pole support 168a which functions as an inside diametercrash stop. FIG. 14 shows the arm assembly 140 rotated to a positionwhere the heads 84 are at the outside diameter of the disks 136 andactuator arm 160 is in contact with dowel 178. FIG. 15 shows actuatorarm 160 in contact with o-ring 180 and the heads 84 at the insidediameter of disks 136.

Actuator assembly 138 provides an average seek time of 25 ms and a trackto track seek time of 8 ms with 1150 tracks per inch. Each disk has 776tracks per surface with 33 blocks per track and 512 bytes per block,providing a formatted capacity of 100 MBytes.

In the embodiments of the present invention described herein the armassembly 40, 140 is pivotably mounted between the top plate 42,142 andthe base plate 32, 132. Nevertheless, other arrangements of the armassembly 40, 140 are contemplated; for example, the arm assembly 40, 140could be mounted to be translated along its longitudinal axis by alinear motor.

During the manufacture of a disk drive in accordance with the presentinvention, efforts must be made to prevent foreign matter from beingenclosed in the controlled environment within the casing 34, 134. Onesource of contaminating particles is the permanent magnets 98, 170which, due to their strength, attract pieces of magnetic material. Thedanger of the presence of magnetic material in the disk assembly 26, 126is two-fold: First, any particle which is present on the disk can causeone of the heads 84 to "crash." Second, a magnetic particle, if in closeproximity with the disks 36, 136, can destroy data which is stored onthe disk in magnetic form. Accordingly, in the second embodiment of thepresent invention, first and second permanent magnets 170a-b areattached to first and second magnet carriers 172a-b (FIG.16). One end ofeach of the magnet carriers 172a-b has a c-shaped end 174 which engageindentations 176a-b in center pole supports 166a. The other end ofmagnet carriers 172a-b are held in position by metal dowel 178 whichextends through the top plate 142 and the base plate 132. Further,screws (not shown) secure the magnet carrier 172a-b to the top and baseplates. The use of magnet carriers 172a-b allows the first and secondmagnets 170a-b to be inserted into the actuator assembly 138 when theassembly of the disk assembly 126 is close to completion, thus limitingthe possibility that the first and second magnets 170a-b will attractmagnetic particles prior to the sealing of the hard disk assembly 126.

Electromagnetic latch 146 of the second embodiment of the presentinvention will be described with reference to FIGS. 16-19. Theelectromagnetic latch 146 includes a latch mount 182, a latch bracket184 which pivots on metal dowel 178 and engages latch tab 186 onactuator arm 160, and a spring 188 for biasing the latch bracket 184 tothe locked position Latch mount 182 has two c-shaped sections 182a-bwhich engage indentations 176c-d in respective ones of the upper andlower center pole supports 168b₁₋₂. Latch mount 182 is furtherpositioned by dowel 178. Thus, dowel 178 has three functions: It servesas the outside diameter crash stop, it serves as the pivot for latchbracket 184, and it serves to position the latch mount 182.

An electromagnet, including a coil housing 190 formed of a magneticallypermeable material and mounted on latch mount 182, and coil 192, is usedto pivot latch bracket 184 to the unlocked position Coil housing 190 hasan outer wall 190a and a center post 190b. When a current is passedthrough coil 192, the magnetic field generated by the coil housing 190attracts swivel plate 194; swivel plate 194 is mounted on the latchbracket 184 so that it can swivel in all directions and be flush withthe outer wall 190a when the swivel plate 194 is captured by theelectromagnet. Contact between the entire outer wall 190a and swivelplate 194 is necessary to provide reliability in the capture of theswivel plate 194. The center post 190b of the coil housing 190 does notextend as far as the outer wall 190a, and a small air gap exists betweenthe center post 190b and the swivel plate 194 to allow the electromagnetto release the swivel plate 194. The air gap is on the order of 1-6thousandths of an inch--preferably 2-4 thousandths of an inch. Withoutthe air gap between the center post 190b and the swivel plate 194, theswivel plate 194 would serve as a magnetic return and it would beextremely difficult to release the swivel plate 194 from theelectromagnet. A high DC voltage is applied to the electromagnet for ashort time to capture the swivel plate 194, and the applied voltage isreduced to a small capture maintenance level. Thus, this structure islow in power consumption and heat dissipation. Further, despite the lowpower consumption of the electromagnet it is highly reliable in itscapture, holding, and release of swivel plate 194, and thus latchbracket 184.

Latch bracket 184 pivots on dowel 178 and has first and second arms 184aand 184b on opposite sides of the pivot. Latch bracket 184 is designedso that it is out-of-balance with respect to the point at which itpivots on dowel 178 to enhance the locking characteristics duringshipping and for nonoperational shocks. Balancing the latch bracketprovides the latch mechanism 146 with positionally independentoperation. Swivel plate 194 is supported by the second arm 184b and thefirst arm 184a contacts latch tab 186. Latch tab 186 has a slopedportion 186a which allows the actuator arm 160 to pivot past latchbracket 184 when the latch bracket 184 is in the locked position; inparticular, latch bracket 184 rides up the sloped portion, pivotingagainst the force of spring 188, as the actuator arm 160 pivots towardsthe inside crash stop 180. FIGS. 15 and 18 illustrate the actuator arm160 locked in position by latch bracket 184, while FIG. 14 illustratesactuator arm 160 pivoted all the way to the outside crash stop 178 withlatch bracket 184 in the unlocked position. A notch 196 is provided infirst arm 184a of latch bracket 184 to allow latch tab 186 to clear thelatch bracket 184 when actuator arm 160 pivots.

The particular embodiment of the latch mechanism 145 described aboveincludes an electromagnet and a swivel plate 194 for pivoting latchbracket 184 to the unlocked position. However, other mechanisms forpivoting the latch bracket could be employed, for example, a solenoid.

The many features and advantages of the disk drive of the presentinvention will be apparent to those skilled in the art from theDescription of the Preferred Embodiments Thus, the following claims areintended to cover all modifications and equivalents falling within thescope of the invention.

What is claimed is:
 1. A rotary actuator for positioning a sensor withrespect to a disk supported by a base plate in a disk drive assembly,comprising:an actuator arm pivotally mounted on the base plate forsupporting the sensor; and voice coil means for pivoting said actuatorarm to position said the sensor with respect to the disk, comprising:afirst planar magnet, attached to and lying in a plane substantiallyparallel to said base plate, for providing a first magnetic field in amagnetic flux circuit including said base plate, a coil, attached tosaid actuator arm, for passing an electric current in the first magneticfield, a magnetically permeable center pole extending through said coil,and support posts attached to opposite ends of said center pole andrespective positions on said base plate for supporting said center pole.2. An actuator according to claim 1, wherein:said voice coil meansfurther comprises:a top plate mounted on said base plate, and a secondplanar magnet, attached to and lying in a plane substantially parallelto said top plate, for providing a second magnetic field in a magneticflux circuit including said top plate; and said coil passes a current inthe first and second magnetic fields.
 3. A rotary actuator according toclaim 2, further comprising:support posts attached to opposite ends ofsaid center pole and respective positions on said top plate, wherein:said top plate, said support posts, and said center pole function as areturn for the second magnetic field; and said base plate, said supportposts, and said center pole function as a return for the first magneticfield.
 4. A rotary actuator according to claim 3, wherein one of saidsupport posts comprises a crash stop to limit the pivoting travel ofsaid actuator arm.
 5. An actuator for positioning a head with respect toa disk rotatably supported by a magnetically permeable base plate in adisk drive assembly, comprising:an actuator arm, pivotally mounted onthe base plate, for supporting the head; a first planar magnet providedon and substantially parallel to said base plate for providing a firstmagnetic field in a magnetic flux circuit including said base plate; acoil provided on the actuator arm and positioned in the first magneticfield; a magnetically permeable center pole extending through themagnetically permeable lower support posts for supporting the centerpole on the base plate.
 6. An actuator according to claim 2, furthercomprising:magnetically permeable upper support posts provided on saidcenter pole; a magnetically permeable top plate supported by said uppersupport posts on the opposite side of the actuator arm from the baseplate; and a second planar magnet provided on and substantially parallelto the top plate for providing a second magnetic field in a magneticflux circuit including said top plate.
 7. A disk drive assembly,comprising:an end plate; a casing attached to said end plate to providea controlled environment within said casing; a magnetically permeablebase plate provided in said controlled environment, mounted on said endplate, and attached to said casing; a disk rotatably mounted on saidbase plate; an actuator arm pivotally mounted on said base plate andhaving first and second ends on opposite sides of the pivotal mount; amagnet assembly, comprising:first and second magnetically permeablesupport posts, a magnetically permeable top plate supported by saidfirst and second support posts, a first planar magnet, mounted on andsubstantially parallel to said base plate, providing a first magneticfield in a first magnetic flux circuit including said base plate, asecond planar magnet, mounted on and substantially parallel to said topplate, providing a second magnetic field in a second magnetic fluxcircuit including said top plate, a center pole formed of a magneticallypermeable material and supported by said first and second support postsbetween said base plate and said top plate, said first and secondmagnetic flux circuits including said center pole; a coil mounted on thefirst end of the actuator arm, said coil surrounding said center poleand having first and second legs provided in respective ones of thefirst and second magnetic fields; and a head mounted on the second endof said actuator arm and adjacent to said disk.